Transient damper for pneumatic sound source employing an electromagnet for controlling its release valve

ABSTRACT

The specification discloses a pneumatic sound source comprising a pressure chamber for receiving gas and having a controllable valve for opening and closing an outlet port. An electromagnet including an electrical coil is energized to hold the valve in its closed position and is deenergized for releasing the valve for the generation of an acoustic pulse. Current is applied to the coil by way of a normally closed switch which is opened to deenergize the coil. Circuitry is coupled across the coil and is actuated, when the valve begins to move following deenergization of the coil, to allow current to flow through the circuitry to shunt the coil, thereby dampening the magnitude of a transient voltage generated by movement of the valve through the path of the decaying magnetic flux.

United States Patent McAlpin [54] TRANSIENT DAMPER FOR PNEUMATIC SOUND SOURCE EMPLOYING AN ELECTROMAGNET FOR CONTROLLING ITS RELEASE [21] Appl. No.: 15,110

[52] US. Cl ..l8l/.5, 307/202 [51] Int. Cl. ..G0lv 1/02 [58] FieldolSearch ..l8l/.5;25l/l41, 129; 200/146;

307/202, 252 K, 252 J; 317/33 SC, 148.5 B

[ Mar. 7, 1972 Primary Examiner-Rodney D. Bennett, Jr.

Assistant Examiner-N. Moskowitz Attorney-+William J. Scherback, Frederick E. Dumoulin, Arthur F. Zobal, Andrew L. Gaboriault and Sidney A. Johnson [5 7] ABSTRACT valve for the generation of an acoustic pulse. Current is applied to the coil by way of a normally closed switch which is opened to deenergize the coil. Circuitry is coupled across the coil and is actuated, when the valve begins to move following deenergization of the coil, to allow current to flow through the circuitry to shunt the coil, thereby dampening the magnitude [56] References Cited of a transient voltage generated by movement of the valve UNITED STATES PATENTS through the path of the decaying magnetic flux. 3,506,085 4/1970 Lo er .l8l/.5 5 Claims, 5 Drawing Figures ON 32 50 Efil''iorr D-C POWER SUPPLY 4 COMMON CONDUCTOR i a2 29 I ae 35b PULSING 0 CIRCUITRY PATENTEUHAR 7 i972 3, 647. O 1 9 SHEET 1 [IF 3 iz-" I COMPRESSOR 2/39 v I R33 li 2" I FIG I 4o 0c POWER I SUPPLY sw|%c: -n-e CIRCUITRY FIG. 4A

COIL CURRENT SILVAN E. MCALPIN INVENTOR ATTORNEY PATENTEUHAR 7 I972 SHEET 2 OF 3 ill" M II E ON N m vm J M S MGW ATTORNEY mmDmmmmm 1 TRANSIENT DAMPER FOR PNEUMATIC SOUND SOURCE EMPLOYING AN ELECTROMAGNET FOR CONTROLLING ITS'RELEASE VALVE BACKGROUND OF THE INVENTION This invention relates to a transient voltage damping system for protecting the switching circuitry employed with a pneumatic sound source having a valve controlled by an electromagnet.

In U.S. Pat. application, Ser. No. 663,800, filed Aug. 28, 1967, by George B. Loper, there is disclosed a pneumatic acoustic source for marine seismic operations and having an electromagnet which is controlled to hold and release the source's gas pressure release valve. The source comprises a chamber for receiving gas and holding gas under pressure. An outlet port is provided through which pressurized gas is released to generate an acoustic pulse. The electromagnet is energized to form a magnetic force for holding the valve in its closed position for confining pressurized gas in the chamber. The flow of current through the electromagnets coil is interrupted to reduce the magnetic force to allow the pressurized gas in the chamber to move the valve to its open position to release the gas to generate an acoustic pulse.

In one embodiment, control means is employed to normally allow electrical current to flow from a voltage source through the coil for energizing the coil to produce the magnetic holding force. This control means is actuated to interrupt the flow of electrical current from the voltage source through the coil to decrease the magnetic force to allow the gas pressure to move the valve to its open position. Following the interruption of flow of current through the coil, the valve begins to move prior to the complete decay of the magnetic flux generated by the electromagnet. The moving valve cuts the magnetic flux and acts as a voltage generator. It has been found that the amplitude of the resulting transient voltage generated, if unlimited or undamped, will damage the control means.

SUMMARY OF THE INVENTION In accordance with the present invention, damage to the control means is avoided by providing circuitry across the coil.

Means is provided for actuating the circuitry to allow electrical energy to flow through said circuitry to shunt the coil when said transient voltage reaches a predetermined level to dampen the magnitude of the transient voltage to protect the control means from a transient voltage of large amplitude.

In one embodiment, the control means is a normally conducting silicon-controlled rectifier while the dampening circuitry includes at least one normally nonconducting siliconcontrolled rectifier.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a pneumatic sound source employed in marine seismic surveying operations;

FIG. 2 illustrates in detail the internal and external structure of the source of FIG. 1;

FIG. 3 is a schematic drawing of the circuitry of the present invention; and

FIGS. 4A and 4B illustrate traces useful in understanding the present invention.

DESCRIPTION OF THE OPERATION OF THE PNEUMATIC SOUND SOURCE Referring now to FIGS. 1 and 2, an acoustic source 20 is shown supported in water from a boat 21 by a cable 22. The acoustic source comprises enclosing wall structure 24 forming a pressure chamber 25 which has an outlet port 26. A quickopening valve 27 of ferromagnetic material is provided for opening and closing the port. A spring 28 is provided for moving the valve to its closed position. An electromagnet comprising an electrical coil 29 and a ferromagnetic core 30 is energized to form a magnetic holding force for holding the valve 27 in its closed position. Electrical current is applied to the coil from DC power supply 32 shown in the enclosed dotted box 33 located on the boat 21. Current is applied to the coil from the power supply 32 by way of a normally closed switch included in switching circuitry 34 and electrical leads 35a and 35b which are coupled to the source.

7 When the valve is in its closed position, the pressure chamber 25 is pressurized with air supplied by air compressor 37. A seal 38 maintains a pressure seal between the core 30 and the valve 27 to seal the pressurized air in the chamber 25. Air compressor 37 is coupled to the acoustic source by conduit 39, solenoid-controlled valve 40, check valve 41, and flexible conduit 42, the latter of which extends to the chamber 25. An acoustic pulse is generated by interrupting the flow of current through the coil 29. When this occurs, the magnetic holding force decreases and the high gas pressure in the chamber 25 rapidly moves the valve 27 to its open position whereby the pressurized gas rapidly flows through chamber port 26 and through venting ports 43 into the water to generate an acoustic pulse. Interruption of the current through the coil 29 is carried out by opening the switch provided in switching circuitry 34. A timer 44 is provided to control the solenoid valve 40 and the switching circuitry 34 to repetitively generate acoustic pulses, for example, at a repetition rate of 5 acoustic pulses per minute.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 3, the switching circuitry 34 comprises a normally conducting silicon-controlled rectifier 45 which allows current to flow through coil 29. Coupled across the coil 29 is a circuit comprising normally nonconducting SCRs 46 and 47. The SCR 45 is turned OFF to deenergize the coil 29. When the transient voltage generated by movement of the valve 27 increases to a predetermined limit, SCRs 46 and 47 are turned ON. This places a low resistance across the coil 29 and damps the amplitude of the transient voltage, thereby protecting SCR 45 from damage.

Current is applied from the plus side of the power supply 32 to the coil 29 by way of conductors 50 and 51, adjustable resister 52, and lead 350. Current then flows to the minus side of the power supply by way of coil 29, lead 35b, resistor 53, conductors 54 and 55, normally conducting SCR 45, conductor 57, and common conductor 58. Resistor 52 is adjusted whereby the voltage from supply 32 is 30 volts or higher. The current which flows through the coil 29 is 10 amperes. The resistance of the coil 29 is about 2.6 ohms whereby 26 volts normally are applied across the coil when it is energized. Thus, a low voltage is applied to the anode of the SCR 45. Transistor 60 normally is conducting whereby a gate voltage normally is applied to the gate of the SCR 45. Thus, SCR 45 normally conducts whereby the coil 29 normally is energized for the production of the magnetic holding force.

In the conducting state of SCR 45, current also flows by way of resistors 63 and 75 to charge capacitor 62. During conduction of SCR 45, the voltage on the left side of capacitor 62 is low; however, the voltage on the right side is relatively high since it is connected to the DC power supply 32 by way of resistor 63.

Current flow through coil 29 is interrupted by firing normally nonconducting SCR 64 and turning OFF transistor 60. When SCR 64 is fired and becomes conducting, the right side of capacitor 62 becomes connected to common conductor 58 whereby the voltage applied to the anode of SCR 45 becomes less relative to that applied to its cathode. Thus, SCR 45 becomes nonconductive. The transistor 60 is turned OFF during the time that SCR 64 is turned ON to remove the voltage from the gate of SCR 45. This is done to prevent the SCR 45 from being retriggered for a short period of time to allow the valve 27 to open properly.

When SCR 45 becomes nonconducting, current flow through the coil 29 is interrupted whereby the magnetic flux produced in the electromagnet decreases in magnitude to a point where the pressurized gas in the chamber 25 is able to move the valve 27 away from the'seal and to its open position to allow the pressurized gas to escape into the water. Cutoff of SCR 45 is only momentary, however, and it becomes conducting again after the valve has moved away from its closed position toward its open position whereby the coil 29 is energized by the time the valve is moved back to its closed position following the generation of an acoustic pulse. In this respect, a pulsing circuit 65 is provided to periodically produce a control pulse to periodically turn SCR 64 ON and simultaneously cut OFF transistor 60. Thus, normally conducting SCR 45 is periodically cut OFF whereby acoustic pulses are periodically generated for exploratory purposes.

Referring now to FIGS. 4A and 48, there are disclosed current and voltage waveforms generated, respectively, during a cycle of operation. The current waveform is that generated through the coil 29, while the voltage waveform is that generated across SCR 45. The time scales of these waveforms are the same but the amplitude scales are different. Current to the coil 29 is interrupted at time a. As the current decreases, the voltage across the coil rapidly increases to maintain the current flowing in its original direction as can be understood by those skilled in the art. Thus, an inductive transient voltage is generated by the coil and reaches a peak of about 280 volts as shown at b in FIG. 4B. When the current decreases to zero and remains there for a period, the inductive voltage across the coil decreases as shown in FIG. 43. Before the voltage decreases to zero, the valve begins to move. The magnetic flux however has not yet completely decayed so that the valve begins cutting magnetic flux and hence causes a large transient voltage and hence current to be induced in the coil beginning at time c. This second transient voltage is in the same direction as the first transient voltage. It has been found that if unlimited or undamped, this second transient voltage reaches a magnitude of about 900 volts and seriously affects the SCR 45 which has a voltage rating of about 600-700 volts.

In order to prevent damage to the SCR 45, circuitry including SCR 46 and SCR 47 is coupled across the coil as mentioned above. Also coupled in series with SCRs 46 and 47 are S-ohm load resistors 68 and 69, respectively. Each of the SCRs 46 and 47 has a voltage rating of about 600 volts and is biased to be in a nonconductive state. The cathode of SCR 47 is coupled to the gate of SCR 46 by way of a lO-kilohm resistor 70. Coupled to the gate of SCR 47 are four Zener diodes 71-74 in series and which are also coupled to conductor 54. Each of the Zener diodes breaks down at about 120 volts. Thus, when the voltage across Zener diodes 71-74 reaches 480 volts, the Zener diodes break down to render SCR 47 conductive which in turn fires SCR 46. When this occurs, a low resistance is placed across coil 29, thereby damping the transient voltage when it reaches about 510 volts across SCR 45. In FIG. 4B, damping occurs at time d. When SCRs 46 and 47 fire, the voltage is dropped across the coil 29 and the shunt load including the total resistance of parallel resistors 68 and 69. The AC impedance of coil 29 is greater than the DC resistance of the shunt load, and hence most of the transient voltage is dropped across the coil 29. When the SCRs 46 and 47 fire, it has been found from measurements that the voltage across SCR 45 drops to about 100 volts. Thus, the second transient voltage is prevented from reaching a level which is above the rating of the SCR 45, thereby preventing the SCR 45 from being damaged by the otherwise large transient voltage generated when the valve begins to move away from its closed position.

The voltage level at the anode of SCR 45 remains at about 100 volts until SCR 45 becomes conductive again. This occurs at time e in FIG. 4B. The voltage across SCR 45 then drops to its normal lower level. At this time, SCRs 46 and 47 become reverse biased and are turned OFF.

During the production of the transient voltage while the SCR 45 is OFF, current flows by way of diode 61 to charge the capacitor 62 to about 510 volts. Capacitor 62 discharges when SCR 45 becomes conductive again. The l-kiloohm resistor 75 limits the amount of flow of current through SCR 45 as the capacitor 62 discharges from its ISO-volt level, thus protecting SCR 45 from the large surge of current while it is conductive.

Referring specifically to FIG. 4A, it can be seen that the current in the coil increases to a maximum as the valve begins to move and then decreases as the valve moves away from the electromagnet. Shortly after the maximum current peak, SCR 45 is turned ON as indicated previously. The current in the coil then decreases to its normal IO-ampere level. As the valve moves back to its closed position, it becomes a current generator again and generates current in the opposite direction until a low peak is reached at time f wherein the valve has been completely seated. Current in the coil then increases to its normal lO-ampere level.

Now that the invention has been described, other components of the circuitry of FIG. 3 will be discussed. The purpose of the diode and ZOO-ohm resister 81 is to dampen the first inductive voltage generated in the coil following interruption of current flow through the coil in order to limit this voltage to a safe value but not delay the opening of the valve 27 unduly.

The pulsing circuitry 65 produces a control pulse once every 12 seconds for controlling the circuitry of FIG. 3. In FIGS. 4A and 4B, the control pulse begins at time a and ends at time d and is employed to render SCR 45 nonconductive during this period. In this respect, each control pulse triggers a light-emitting diode 82 which in turn causes transistor 83 to conduct, which is normally nonconducting. When this occurs, transistors 84 and 85 are turned ON, while transistor 86 is turned OFF. Normally, transistors 84 and 85 are OFF, while transistor 86 in ON. When transistor 86 is turned OFF (time a in FIGS. 4A and 48), a voltage is applied to the gate of SCR 64 to turn this SCR ON. When transistor 85 is turned ON (time a in FIGS. 4A and 4B), the voltage normally applied to the base of transistor 60 is reduced, thereby turning transistor 60 OFF to remove the voltage from the gate of SCR 45. Thus, SCR 64 is turned ON at time a. When the control pulse terminates, SCR 64 is turned OFF and transistor 60 is turned ON whereby SCR 45 is rendered conductive again at time d.

The purpose of circuitry illustrated at 90 is to allow the operator to monitor the current produced across resistor 53 and hence in coil 29 and to obtain a time break for seismic data processing purposes. The monitor is illustrated at 91.

The diodes 92 and.93 each have a rating of about 0.7 volt whereby they break down when the voltage across resistor 53 increases above 1.4 volts. The normal ten amperes of current flow through the coil 29 does not cause these diodes to break down. However, when the second transient voltage is generated and the voltage across 53 increases above 1.4 volts, diodes 92 and 93 break down and a pulse is obtained through transformer 94. This pulse is applied to circuitry illustrated at 95 and is employed for time break purposes.

Referring again to FIGS. 1 and 2, there will be described more of the mechanical details of the source and equipment. Cable 22 is coupled to a harness which in turn is coupled to nose number 101 and the vertical tail fin 102. Also coupled to the harness is a strain cable 103 which extends to the boat 21 and is securely affixed to the boat at 104. The cable 22 is supported at the end of the boat by a reel 105 and a winch 106. A motor and a reel system 107 is employed to reel the cable 22in and out to raise and lower the source, respectively. The conduit 42, electrical leads 35a and 35b, and cable 103 are bound together by tape to form a flexible and lightweight conduit 108 which is let out and pulled in by hand.

At the source, the conduit 42 extends through tubing 110 coupled to the harness 100 and then to an inlet 111 which leads to the pressure chamber 25. The electrical leads 35a and 35b extend through a tube 112 coupled to the harness and then through smaller tubes 113 and 114 coupled to the harness and to the source. The electrical leads 35a and 35b then extend to a terminal box 115 where they are connected to the two ends of the electrical coil 29. The electrical coil 29 is secured in a slot 116 formed in the core 30.

Coupled to the backend of the valve 27 by machine screws 118 is a cylinder 119 which guides the valve 27 in its 'movement and also supports one end of the spring 28. Cylinder 119 is supported for movement by hearing 120 located in cylinder 121. Cylinder 121 is coupled to the core 30 by an arrangement including annular plate 122 and cylinder 123 in which the venting ports 43 are formed. Cylinder 123 is welded to annular plate 122 and is coupled to the core 30 by machine screws 124. The other end of the spring 28 is supported in an annularshaped member formed by cylinder 126 coupled to cylinder 127 by way of spokes 128. Cylinder 127 in turn is threaded into cylinder 121. Secured to the exterior of cylinder 121 is an annular member 130. A truncated, cone-shaped member 131 is coupled to annular plate 122 and annular member 130 for additional support for the back end portion of the source. A plate 132 is coupled to annular member 130 by way of machine screws 133. Coupled to the plate 132 are the fins 102, 135, and 136.

The valve 27 is slowed and stopped at the end of its opening movement by water located in a deceleration container formed by plate 122 and the back end of cylinder 123. The outside diameter of valve 27 is slightly smaller than the interior diameter of cylinder 123 whereby water may flow between these members. As the valve moves within the deceleration container, water is squeezed between the outside surface of the valve and the inside surface of the container to decelerate the valve. Water within cylinder 119 may flow by way of apertures 137 extending through cylinder 1 l9 and by way of aper'- ture 138 extending through plate 132.

In one embodiment, the seal 38 employed in the source may be of the type mentioned in US. Pat. application, Ser. No. 663,800. It is held by member 140 which is secured to core 30 by machine screws 141. Seal 38 forms a seal with metal plate 142 secured to the valve 27 by way of member 143 and machine screw 144. Wire member 145 coupled to screw 144 and to rod 146 prevents screw 144 from turning.

Timer 44 (FIG. 1) is coupled to circuitry 34 and to valve 40 by way of conductors 44a and 44b.

What is claimed is:

1. In a system for carrying out marine seismic operations useful in the investigation of underwater formations comprismg:

an acoustic source comprising a gas pressure chamber formed of rigid wall structure having an outlet port for releasing high gas pressure rapidly from said chamber to generate an acoustic pulse in water; valve means movable to open and close positions for opening and closing said outlet port, respectively; an electromagnet comprising an electrical coil for producing a magnetic holding force for application to said valve means; and valve retract means for moving said valve to said closed position following the generation of an acoustic pulse,

a source of electrical energy to be coupled to said electrical coil by way of electrical conductors, the combination therewith of:

control means for controlling the application of electrical energy from said source to said coil,

said control means nonnally allowing electrical current to flow from said source through said coil for energizing said coil to produce said magnetic holding force to hold said valve means closed for confining said gas under pressure in said chamber,

means for controlling said control means to interrupt the flow of electrical current from said source through said coil to decrease said magnetic force to allow said gas pressure to move said valve means to its open position to release pressurized gas from said chamber to generate an acoustic pulse,

said valve means upon movement toward said open position resulting in the generation of a large transient voltage is said coil prior to the decay of magnetic flux in said electromagnet following the interruption of the flow of electrical current through said coil means coupled across said cod for dampening the magnitude of said transient voltage, and

means for actuating said dampening means when said transient voltage reaches a predetermined level to damp the magnitude of said transient voltage to protect said control means from said transient voltage.

2. The combination of claim 1 wherein:

said dampening means comprises at least one normally nonconducting silicon-controlled rectifier.

3. The system set forth in claim 1 wherein:

said dampening means has a direct current impedance which is less than the alternating current impedance of said coil.

4. The system set forth in claim 2 wherein:

said actuating means comprises at least one Zener diode for controlling the conduction of said silicon-controlled rectifier.

5. The system set forth in claim 1 wherein:

said control means comprises a normally conducting silicon-controlled rectifiier.

UNITED STATES PATENT OFFICE CETIFICATE @F CQREQTION Patent No, Dated March 7, Inventor-(s) Silvan E McAlpin It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3 line 25, after "at" and before "2'', --time-- should be inserted,

4, line 1, "l50-volt" should be --5l0-volt--;

line 31, "in" should be --is-'.

Column 5, line 15, "back end" should be --backend-.

Column 6, line 23, "is" should be -in--.

Column Signed and sealed this 20th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-105O (10-69) USCOMM-DC 60376-P69 U.S. GOVERNMENT PRINTING OFFICE: I969 O366-334 Patent No.

Dated March 7, 1972 Inventor(s) Silvan E. McAlpin Column 4,

Column 5, Column 6,

Signed and (SEAL) Attest:

EDWARD M.FLETCHER, Attesting Officer It is certified that error-appears in the above-identified 'patent and that said Letters Patent are hereby corrected as shown below:

ROBERT GOTTSCHALK Commissioner ofjPatents FORM PO-IOSO (10-69) I USCOMM-DC 60376-P69 fi u.s. GOVERNMENT PRINTING OFFICE: [969 o-3ss-3a4 

1. In a system for carrying out marine seismic operations useful in the investigation of underwater formations comprising: an acoustic source comprising a gas pressure chamber formed of rigid wall structure having an outlet port for releasing high gas pressure rapidly from said chamber to generate an acoustic pulse in water; valve means movable to open and close positions for opening and closing said outlet port, respectively; an electromagnet comprising an electrical coil for producing a magnetic holding force for application to said valve means; and valve retract means for moving said valve to said closed position following the generation of an acoustic pulse, a source of electrical energy to be coupled to said electrical coil by way of electrical conductors, the combination therewith of: control means for controlling the application of electrical energy from said source to said coil, said control means normally allowing electrical current to flow from said source through said coil for energizing said coil to produce said magnetic holding force to hold said valve means closed for confining said gas under pressure in said chamber, means for controlling said control means to interrupt the flow of electrical current from said source through said coil to decrease said magnetic force to allow said gas pressure to move said valve means to its open position to release pressurized gas from said chamber to generate an acoustic pulse, said valve means upon movement toward said open position resulting in the generation of a large transient voltage is said coil prior to the decay of magnetic flux in said electromagnet following the interruption of the flow of electrical current through said coil, means coupled across said coil for dampening the magnitude of said transient voltage, and means for actuating said dampening means when said transient voltage reaches a predetermined level to damp the magnitude of said transient voltage to protect said control means from said transient voltage.
 2. The combination of claim 1 wherein: said dampening means comprises at least one normally nonconducting silicon-controlled rectifier.
 3. The system set forth in claim 1 wherein: said dampening means has a direct current impedance which is less than the alternating current impedance of said coil.
 4. The system set forth in claim 2 wherein: said actuating means comprises at least one Zener diode for controlling the conduction of said silicon-controlled rectifier.
 5. The system set forth in claim 1 wherein: said control means comprises a normally conducting silicon-controlled rectifiier. 